Room temperature electronic absorption

Figure 5.7 Room-temperature electronic absorption, excitation and emission spectra for 2 in aqueous solution. The excitation spectrum of 2 was recorded by monitoring emission at 400 nm. Reproduced with permission from [31]. Copyright (2004) Royal Society of Chemistry.

Figure 10.8 Room temperature electronic absorption spectrum recorded on a THF solution of 6. Bands are marked by the nominal Russell-Saunders multiplet to which the excitation occurs. (Adapted from Ref. [34], Copyright (2011) Nature Publishing Group.)...

Figure 24 displays the high energy (E > 25,000 cm-1) region of the room temperature electronic absorption spectrum for Zn(bpy)(tdt), where bpy = 2,2 -bipyridine. The LLCT transition occurs at 22,470 cm-1 (445 nm) with very weak absorption intensity (e = 72 M 1cm 1). The origin of the weak LLCT is a function of the symmetry of this psuedo-tetrahedral complex. A MO diagram for Zn(bpy)(tdt), derived from extended Hiickel calculations, is presented in Fig. 25. Irrespective of whether the metallo(diimine)(dithiolene) complex is square-planar or psuedo-tetrahedral, the point symmetry is C2V, and all intermediate geometries possess C2 symmetry. When the dithiolene and diimine planes are orthogonal (psuedo-tetrahedral geometry) the HOMO — LUMO transition represents a b2 —> b one-electron promotion and is electric dipole forbidden. However, the HOMO —> LUMO transition in a square-planar...

Figure 29. Room temperature electronic absorption spectra of the [Ni(S2C2Me2)2]° 1 2 complexes in acetonitrile. [Adapted from (328).] Solid line [Ni(S2C2Me2)2]° thin line ...

Figure 1 Spectral characteristics of oxidized Cu, Zn SOD (a) X-band EPR spectrum, 77 K (Used with permission from Ref 1. 1985 Division of Chemical Education, Inc) (b) room-temperature electronic absorption spectrum [protein] = 35mgmL ...

Figure 8.2 Room temperature electronic absorption spectra.

TTF)5Pt(CN)4.2 CH3CN (1) In this compound (Fig. la), the unit cell contains two independent Pt(CN)4(TTF)2 5 blocks [6]. The TTF molecules of each independent unit form centrosymmetric isolated pentamers. The Pt(CN)4 " dianions are separated by the disordered acetonitrile molecules. The structural features of the TTF molecules show that the central molecule of the pentamer is neutral, while the other four are fully oxidized, indicating mixed valence in the isolated pentamers. This new pq>e of organization has particular optical properties. The room-temperature electronic absorption spectrum (Fig. 2) e ibits the two... 

Figure 6.11 Room temperature electronic absorption spectra of the homoleptic compounds M2(02CBu )4 and M2(02CPh)4, where M = Mo or W, recorded in THF solution. (Reprinted with permission from Ref. [66]. Copyright 2012 American Chemical Society.)...

At room temperature, flash absorption studies revealed that an electron acceptor designated Aj was functioning under conditions where F and Fg were presumably reduced [37]. The state (P-700, A2 ) is formed upon flash excitation and recombines with tiu — 250 jUS. The difference spectrum due to its formation was analysed into contributions of P-700 and A2. The latter includes mainly a small and broad bleaching around 430 nm, and perhaps some absorption shifts in the red. These absorption properties, together with the disappearance of the A2 absorption signal when iron-sulfur proteins are denatured [38,39], indicate that Aj may be an iron-sulfur centre. 

J Rawlings, 0 Siiman and HB Gray (1974) Low temperature electronic absorption spectra of oxidized and reduced spinach ferredoxins. Evidence for nonequivalent iron (III) sites. Proc Nat Acad Sci, USA 71 125-127 K Brettel (1988) Electron transfer from Af to an iron-sulfur center with t% = 200 ns at room temperature in photosystem I. FEBS Lett 239 93-98. 

An intervalence electron-transfer band, not present in the Fe analogue, was observed in the room temperature electronic spectrum at 13 800cm . Mossbauer spectra indicated distinct Fe" and Fe " sites at 17K while at 300 K a single absorption was observed. The thermal barrier to electron transfer in the trimer was estimated as about 470 cm. Triiron clusters of this type, in the presence of zinc powder, acetic acid, aqueous pyridine and oxygen, are reported " to effect the oxidation of saturated hydrocarbons. The exchange interactions in the series of complexes [Fe2 M 0(02 CMe)spyj] py (M = Mg, Mn, Co, Ni or Zn) which, M = Ni excepted, are isomorphous with the mixed valence complex referred to above have been measured. 

Although UFg has a conveniently high vapor pressure at room temperature, its absorption spectrum is much more complex than that of the metal because of the large number of vibrational and rotational states superposed on each electronic state. Moreover, at room temperature these bands are broadened sufficiently to preclude selective absorption. 

Room and low-temperature electronic absorption spectra for the (110) face of a Os2piv4Cl2 crystal are shown in Figs. 3 and 4. No absorption attributable to electronic transitions could be found in the 1300-2000 nm region. Strong vibrational overtone absorption prevents extension of the measurements beyond... 

Room temperature optical absorption spectra of transition metal ions in solution or in the solid state mostly consist of broad bands from which little information can be obtained. Dorain, Patterson and others [1-4] reported more than twenty years ago that when complex ions such as ReCl, with broad room temperature absorption bands, are doped as impurity ions into suitable host lattices and cooled to low temperatures the broad absorption bands are sometimes resolved into a series of sharp vibronic lines. In a classic study in 1966, Dorain and Wheeler reported the optical absorption spectra of mixed K2(Re,Pt)Cl6 and Cs2(Re,Zr)Cl5 single crystals at 4.2 K. In this case the 5d ReCll ion is doped as a substitutional impurity into the K2PtCl6 and Cs2ZrCl6 host lattices. Information was obtained about the nature of the observed electronic transitions, the excited electronic state vibrational energies and the magnetic properties of the low-lying excited electronic states. 

Metal oxide electrodes have been coated with a monolayer of this same diaminosilane (Table 3, No. 5) by contacting the electrodes with a benzene solution of the silane at room temperature (30). Electroactive moieties attached to such silane-treated electrodes undergo electron-transfer reactions with the underlying metal oxide (31). Dye molecules attached to sdylated electrodes absorb light coincident with the absorption spectmm of the dye, which is a first step toward simple production of photoelectrochemical devices (32) (see Photovoltaic cells). 

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